Substrates are used in a variety of applications, such as buildings, automobiles, appliances, etc. Oftentimes, the substrates are coated with a functional coating(s) to exhibit the required performance properties. Examples of functional coatings include electroconductive coatings, photocatalytic coatings, thermal management coatings, hydrophilic coatings, etc.
A photocatalytic thin film coating can be applied on a substrate, such as glass, to keep the surface free of common organic surface contaminants. Known photocatalytic thin film coatings include those made of titania (TiO2). When the titania coating is exposed to ultraviolet radiation (“UV”), it exhibits photocatalytic properties. Specifically, the coating absorbs UV photons and, in the presence of water or moisture, generates highly reactive hydroxyl radicals that tend to oxidize organic materials on the coated substrate. Ultimately, any organic material on the surface of the coated substrate gets converted to more volatile, lower molecular weight materials that can be washed away or evaporate away.
Typically, the functional coating is deposited directly on the substrate. In many instances when a functional coating is applied the traditional way, the coated substrate exhibits less than optimal durability and undesirable aesthetic properties. Examples of undesirable aesthetic properties include increased reflectance and/or unwanted color. As a result of undesirable aesthetic properties, it is not practical to deposit many functional coatings at their optimal thickness. For example, it is not practical to deposit a photocatalytic coating at the thickness that produces the greatest photocatalytic activity due to unwanted color or high reflectance.
The present invention provides a coated substrate that includes an undercoating and a functional coating that is applied over the undercoating. The coated substrate according to the present invention can exhibit improved performance properties, such as aesthetic properties, durability, photocatalytic activity, etc.